Tamper-evident closures for containers such as bags, envelopes, packages, etc. and tamper-evident tapes and labels for use with bags, envelopes, and other packages have been available for several years. Generally, if these existing closures are forced open, the visual appearance of the closure changes so as to provide an indication that the contents of the container have been accessed. Containers fabricated having tamper-evident closures are commonly used in industries in which the contents of the containers must be maintained in tight security, for example, in the banking industry. In certain instances package manufacturers employ prefabricated closures in the form of a tape or label to provide a tamper-evident closure on their packaging. Tamper-evident closures in the form of tapes or labels are also often used by everyday consumers who want to ensure that their packages are securely sealed and will evidence tampering if it occurs.
One form of container commonly used in banking and other industries is a bag, pouch or envelope (generally referred to herein as a bag) formed of a plastic material such as polyethylene. The opening in this type of bag is commonly closed with a pressure-sensitive adhesive located on one side of the bag. To close the bag, a peel-back strip covering the free side of the adhesive is removed, and the exposed surface of the adhesive is then pressed against the opposite side of the bag. Generally, if a bag of this type is later forced open, the pressure-sensitive adhesive and/or other parts of the bag will distort and break apart, so as to provide an indication that the bag has been opened, possibly without authorization. Closures for a bag of this type have been formed with layers in addition to the pressure-sensitive adhesive to provide a clearer indication of when the closure is forced open. For example, U.S. Pat. No. 5,060,848 to F. R. Ewan describes a tamper evident seal that uses a layer of nitrocellulose or acrylic ink that breaks apart in a selected pattern when the seal is forced open. The layer of ink is adhered to a polyester panel that is part of the seal. Before applying the ink, the plastic panel is masked with a desired pattern of a silicon oil releasant material, which normally causes the ink to break apart in the masked pattern when the seal is forced open. Also, to ensure that the ink layer adheres to the silicon oil releasant material and polyester panel, a primer is applied over the silicon oil releasant, and the ink is then applied over the primer.
Unfortunately, bags of this type are generally expensive to manufacture, use hazardous materials, and are not easily recycled. For example, the polyester panel disclosed in U.S. Pat. No. 5,060,848 to F. R. Ewan is not easily recycled, and the primer required is hazardous. Furthermore, thieves have devised a scheme to gain access to the contents of bags of this type without detection. The scheme devised involves spraying a liquid refrigerant onto the adhesive to freeze the adhesive down to its transition temperature, generally at about -10.degree. F. At this temperature, the adhesive becomes brittle and loses its adhesive qualities, i.e., tack. The thief is then able to open the bag and remove certain contents. The thief allows the adhesive to warm back to room temperature, at which point the adhesive regains its tack, and then simply recloses the bag by applying pressure, all without any evidence of tampering.
Tamper-evident closures for plastic bags have been formed to combat the problem of refrigerant tampering. Such closures provide an indication that the bag was opened, whether or not a refrigerant is first applied. These closures include multiple adhesive and nonadhesive layers that have differing strengths so that when the closure is forced open, one or more of the layers is permanently altered, even if a refrigerant is first applied. For example, U.S. Pat. No. 4,834,552 to K. R. Makowka describes a tamper-evident seal for a plastic envelope. The tamper-evident seal comprises two paper layers and an adhesive layer. One of the paper layers is bonded to a closure flap on the back wall of the envelope, the other paper layer is bonded to the front wall of the envelope, and the adhesive layer is applied to the free side of one of the paper layers. To close the envelope, the closure flap is folded over the envelope opening, and the adhesive layer is pressed onto the paper layer that has a free side. The adhesive seeps into the interstices of the paper layers to form a mechanical-type lock with the paper layers. The strength of this mechanical-type lock is apparently greater than the internal strength of the paper layers, even if a refrigerant is first applied, so that the paper layers break apart when the seal is forced open.
Unfortunately, closures such as the seal disclosed in the Makowka patent have several shortcomings. These closures do not provide any evidence of refrigerant tampering unless the closure is actually forced open. Thus, if a thief begins to attempt to open a bag by applying a refrigerant, but his efforts are somehow thwarted before he is able to force the bag open, the thief's tampering will go undetected. Even if these closures are forced open, they do not always satisfactorily provide evidence of such tampering. Any delamination of one of the paper layers can only be detected by close inspection; the delamination is not bold and distinct as would be desired. Once the closure is forced open, it is possible to use additional adhesive/glue to reclose the closure, without any readily visible evidence that the closure was ever opened. In addition, these closures generally have high production costs. For example, in addition to an adhesive layer as is commonly used to close plastic bags, the closure described in the Makowka patent requires two paper layers, which must both be bonded to the envelope during its production. Furthermore, the bag and closure taught by the Makowka patent is not readily recyclable.
To overcome these shortcomings in the existing technology, what is needed is a closure in the form of a tape or label that provides evidence of forced opening of a seal created by the tape or label, regardless of whether a refrigerant is applied, and additionally, provides evidence of refrigerant tampering, regardless of whether the closure is actually opened. The tape or label should be easy to close, and the evidence of tampering provided should be readily visible, i.e., bold and distinct. Furthermore, the tape or label providing these features should also be relatively inexpensive and easy to recycle and include only nonhazardous materials. As explained in the following, the present invention provides a tape and label that meets these criteria.